Magnetic fabrics from the Costa Rica margin; sediment deformation during the initial dewatering and underplating process

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doi: 10.1016/S0012-821X(02)01076-2
Author(s): Housen, Bernard A.; Kanamatsu, Toshiya
Author Affiliation(s): Primary:
Western Washington University, Pacific Northwest Paleomagnetism Laboratory, Bellingham, WA, United States
JAMSTEC, Yokosuka, Japan
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 206(1-2), p.215-228. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 24 refs.; illus., incl. sect., sketch map
Summary: Drilling off of the Costa Rica margin during Ocean Drilling Program Leg 170 penetrated the complete sediment section seaward of the Middle Americas Trench (MAT) at one location (Site 1039), and sections through the margin wedge, decollement, and subducting sediments at two locations (Sites 1040 and 1043) near the toe of the wedge. Analyses of these sediments and their structures indicated that the margin wedge is not constructed by offscraping of the present incoming sediments, but is an older (perhaps accreted) structure. Nearly the entire section of sediments entering the MAT is thrust beneath the margin wedge. Anisotropy of magnetic susceptibility (AMS) and paleomagnetic data provide insight into the initial stages of fabric development associated with formation of the active decollement fault. Within the decollement zone, fabric development is localized to the upper few meters of the decollement, as indicated by higher AMS P values and by fabric orientations. Below the decollement, the uppermost 180 m of the underthrust hemipelagic sediment section is also deformed, as indicated by comparison of fabrics and their orientations between the seaward reference site and the sites that penetrated the decollement. AMS foliations become progressively more anisotropic, and the orientation of these fabrics, following reorientation of the cores using paleomagnetism, dip landward within the underthrust sediment package. These data indicate that deformation involves thinning of the incoming sediment package by compaction produced by distributed shearing of the upper portion of the sediment package. The fabric data suggest that the uppermost 180 m of the underthrust sediments are undergoing incipient underplating beneath the margin wedge. Abstract Copyright (2003) Elsevier, B.V.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Accretionary wedges; Active faults; Central America; Continental margin; Costa Rica; Decollement; Dehydration; East Pacific; Fabric; Faults; Geophysical profiles; Hemipelagic environment; Leg 170; Magnetic susceptibility; Marine environment; Marine sediments; Middle America Trench; North Pacific; Northeast Pacific; ODP Site 1039; ODP Site 1040; ODP Site 1041; Ocean Drilling Program; Pacific Ocean; Plate convergence; Plate tectonics; Sediments; Seismic profiles; Subduction; Underplating; Underthrust faults
Coordinates: N093943 N093943 W0861045 W0861045
N093823 N093823 W0861200 W0861200
N093916 N093916 W0861109 W0861109
Record ID: 2003022460
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands